Chip closes distance to real-time 3-D images

PORTLAND, Ore.  The problem with machine vision is that the cameras are two-dimensional recorders of three-dimensional scenes. Objects in an image may be obscured by lighting, occluded by obstacles or camouflaged by similar colors in the background. Sophisticated software can sometimes piece together objects from subtle cues, such as when two camera positions are used to reveal parallax. But such algorithms take time to run, making them inappropriate for real-time applications, like automobile collision avoidance.

Now one company claims to have solved the problem with a real-time 3-D camera that uses pixel-level hardware to reveal the distance to any object in any scene, regardless of lighting, occlusion or blending. By integrating 3-D hardware into its SunShield CMOS 3-D time-of-flight imaging sensors, Canesta Inc. (Sunnyvale, Calif.) says it enables machine vision cameras that perceive objects, rather than just sense images, in a scene.

"We have been perfecting this technology since 1999, and we have finally cleared the last hurdle to commercialization," said Canesta CEO and president James Spare. "Our first application is slated for release in the fourth quarter of 2007."

Conventional image chips work by virtue of semiconductors that generate free electrons in response to light falling on them. Canesta's CMOS image sensor works the same way, but it is integrated with an infrared light-emitting diode that illuminates the scene with invisible light. Circuits built into each pixel time how long it takes the infrared light to reach an object. Those calculations yield a 3-D depth map for an entire scene in real-time.

"Our technology can perceive in 3-D using a true CMOS process. We do it by detecting phase delay to measure time of flight, which is proportional to the distance traveled, for each pixel in a scene," said Canesta CTO Cyrus Bamji.

The infrared light source in the Canesta approach sends out a 50-MHz pulse train. Each pixel is provided with a clock synchronized with the light source. It outputs two signals, which are integrated onto two capacitors. From the voltage difference between the capacitors, the phase can be determined to better than one part in 300, or less than 50 picoseconds, according to Canesta.

The SunShield technology enables the distance measurement to be made independently of how a scene is lit. It works even if lighting conditions are extremely bright100k luxand even if the shutter time is long and the lighting conditions quickly change from dark to light.